V-ribbed drive belt. BMW engine.
Click for larger image.
Water pump driven by a drive belt.
Badly worn drive belt. You can see cracks and
missing chunks. Click for larger image.
Self-adjusting drive belt tensioner.
A drive belt is used to drive accessories installed on your car engine, such as the alternator, water pump, power steering pump and the air conditioner compressor. Sometimes a drive belt could also be called a "serpentine belt" or "accessories belt." Most modern cars have one or two drive belts. Older cars used V-shaped belts, while today's cars use V-ribbed belts that are flat on one side and have ribs on the other side (see the photos).
Drive belt problems
A drive belt is made from very flexible and durable material, but it still wears over time. On average, a drive belt can last for 3-4 years. Improper tension, excessive heat, oil or coolant leaks cause the drive belt to wear faster. A worn out belt may cause squeaking or chirping noise and a badly worn out belt can break.
What happens if the drive belt breaks
If the drive belt breaks, all the accessories driven by the belt will stop, basically leaving you waiting for a tow truck. In many cars a drive belt drives a water pump and power steering pump. If the drive belt breaks, the engine will overheat as the water pump will stop moving the coolant into the radiator to cool it down. A car will also lose a steering assist and the steering will become very hard. For this reason it's important not to overlook a drive belt during a regular maintenance and replace it at recommended intervals.
A drive belt also needs to be replaced if it shows any damage, such as cracks, tears, cuts, etc. (see the photo). It's also a good idea to replace a drive belt before a long road trip, especially if it's been a while since it was changed last time. Read more: Car checklist before a long trip.
Drive belt tensioner
Over time, the drive belt stretches. To compensate for this there is a belt tensioner that keeps the drive belt under proper tension. In some older cars, a belt tensioner had to be manually adjusted from time to time. If not adjusted in time, the belt would get loose and start slipping, making a loud whistling or squeaking noise. Commonly you would hear this noise when the car is just started cold in the morning or when turning the steering wheel all the way left or right to the limit. Newer cars have a drive belt with a spring-loaded self-adjusting tensioner that maintains the proper belt tension automatically.
Drive belt replacement
A drive belt is not very expensive part and usually doesn't cost much to replace. Roughly, a drive belt replacement in a garage could range from $90 to $180. On most cars it's a fairly simple job that typically takes no more than 30-40 minutes. If you want to replace a drive belt yourself, you will need a drive belt diagram. One way to get it is to draw a diagram from the existing belt.
A: If you said that the noise started after the alternator has been replaced, we would recommend to recheck the alternator installation. The noise you describe could happen when the belt pulleys are not aligned properly. Maybe the alternator was not installed correctly or the belt pulley on the alternator is not seating properly.
A: It could be a failing belt tensioner which was a common problem in this car. Have it checked out.
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